Glass spacing sticks for dry type transformer



Sept. 15, 1959 a. J. JOHNSTON 2,904,750

GLASS smcmc STICKS FOR DRY TYPE TRANSFORMER Filed Dec. 30, 1955 2 Sheets-Sheet l r E w i Sept. 15, 1959 G. J. JOHNSTON GLASS SPACING STICKS FOR DRY TYPE TRANSFORMER 2 Sheets-$heet 2 Filed Dec. 30, 1955 United States Patent GLASS SPACING STICKS FOR DRY TYPE TRANSFORMER Gorman J. Johnston, Pittsburgh, Pa., assignor to Aliis= Chalmers Manufacturing Company, Milwaukee, Wis.

Application December 30, 1955, Serial No. 556,678

1 Claim. (Cl. 336-60) This invention relates in general to transformers and in particular to an improved arrangement for providing cooling ducts in the winding assembly of a transformer or similar device.

Most transformers because of the characteristics of the insulation employed in the winding assembly are limited to a maximum operating temperature, usually expressed in so many degrees rise over ambient. This limitation is imposed to prevent excess aging of the insulation which occurs relatively fast if .the assembly operates above the critical temperature of the insulation for any period of time.

In order to increase the ability of the winding assembly to dissipate heat more rapidly and thereby operate at a higher rating without damage to the insulation, the prior art has suggested various ways for providing cooling ducts between the coils of the winding, thus subjecting more surface of the winding to a cooling medium.

Usually cooling ducts are provided in the winding assembly by inserting spacers between adjacent coils of the winding. If, for example, the winding assembly includes a number of concentric cylindrical type coils, adjacent coils are usually separated radially by spacing sticks which extend parallel to the axis of the winding and are spaced circumferentially around the cylindrical surfaces of the coils.

In transformers whose windings are designed to operate at relatively high temperatures, the spacing sticks necessarily have to be made of a material which is heat resistant and also maintains its dielectric strength at relatively high temperatures. The material should also be inexpensive -for economic purposes. Various materials have been suggested by the prior art but none of these materials meet the above three mentioned requirements. For example, silicon impregnated asbestos millboard can withstand temperatures up to 180 C. but it is dielectrically weak and has a high rate of moisture absorption. It is also fairly expensive. Laminated glass blocks made from glass mats woven from glass fibers or the like, or from woven glass webbing impregnated with a silicon varnish and binder also have been suggested. However, owing to its destructive effects on cutting tools these materials are quite expensive.

Because of the relatively good heat resistant characteristics of glass and its relatively inexpensiveness, attempts have been made to use glass sticks as coil spacers. However, glass is mechanically weak and has a tendency to break during the winding operation causing the broken portions of the glass spacer to change position. In addition, there is a tendency for the ends of the glass spacers when broken to puncture the insulation resulting in electrical failure of the transformer when energized.

According to the present invention the above mentioned disadvantages of glass spacing rods are overcome by providing a sleeve around the spacing sticks, the sleeve being made substantially of woven inorganic fibers, such as glass fibers. Material known in the art as Fiberglas fabric has proved quite successful. Such an ar- 2,904,760 Patented Sept. 15, 1959 rangement adds considerable strength to the glass rod and in the event a spacing stick should break during the winding operation the sleeve protects the portion of the broken rod from moving and prevents the insulation from being punctured. This arrangement is also capable of withstanding temperatures of C. rise over ambient.

It is therefore an object of the present invention to provide an improved winding arrangement for a stationary induction apparatus operating at relatively high temperatures.

A further object of the present invention is to provide in a winding assembly subjected to relatively high operating temperatures an improved arrangement for providing cooling ducts.

A further object of the present invention is to provide an improved coil spacer which is inexpensive to manufacture and is mechanically and dielectrically strong at relatively high temperature.

Objects and advantages other than those mentioned above will become apparent from the following description when read in connection with the drawing in which:

Fig. 1 is a view in elevation partly in section of a transformer embodying the improved coil spacers;

Fig. 2 is a plan view of the transformer shown in Fig. 1; and

Fig. 3 is an isometric view of a portion of the winding assembly of thetransformer shown in Fig. 1.

Referring to the drawing, the transformer shown in Fig. 1 comprises generally a magnetic core 11 and similar winding assemblies 12 and 13 disposed on each leg 14 of core 11. Each winding assembly comprises a low voltage winding section 15 and a high voltage winding section 16. Since the assemblies 12 and 13 are similar, only one assembly is described in detail. As shown, low voltage section 15 of the winding assembly 12 comprises a plurality of coaxially disposed cylindrical type coils 17a and 17b and a plurality of glass spacer sticks 18 which are disposed with respect to the coils 17 to provide a plurality of cooling ducts. 19 throughout the low voltage section 15. r The glass spacing sticks 18, asshown more readily in Fig. 3, are grouped in. pairs with each pair of rods enclosed within a separate sleeve 20. The sleeve is made of Fiberglas material which has the required heat and dielectric characteristics. In additionnto having these desired characteristics, Fiherglas material also has little or no tendency to tear in the event one of the rods should'break during the winding operation.

Preferably the sleeve 20 covers a pair of glass rods 18 but if desired only one rod 18 may be used. The use of a pair of rods 18 tends to prevent chording of the coil member or insulation member immediately surrounding the spacers 18. If only one rod is used or the distance between spacers is too great, the coil and insulation of the next layer will tend to straighten out into a chord rather than follow a curved path. Such chording is undesirable because it causes the member being wound to depart from the strongest possible mechanical construction which is a circle, and also reduces the area of the cooling ducts 19 established by the spacers 18.

Each low voltage winding section 15 comprises two cylindrical coils 17a and 17b which are wound on a cylindrical form 21. A plurality of sleeved glass rods 18 are disposed between the form 21 and the first coil 17a of the low voltage section 15. The second coil 17b of the low voltage winding may be wound directly over the first coil and additional sleeved spacers 18 provided on the outside cylindrical surfaces of the second coil 17b.

If the low voltage winding comprises more than two coils the construction is repeated so that at least one side of each coil is adjacent the cooling ducts. Insulation between contiguous coil layers is. achieved by the turn to turn insulation of the wire from which the coil is wound. This insulation may be of any suitable type known in the art, depending on the operating temperature of the winding,

The high voltage section 16 may comprise a plurality of disk type coils 22 spaced from the low voltage winding by insulation referred to as the high to low barrier 23. ooling ducts 19 are preferably provided on each side of the barrier '23. in ajmanner similar toy that previously described. As shown, pairs of sleeved spacing sticks 18 are spaced circumferentially around the outer cylindrical surface of the outer coil 17b of the low voltage section and the barrier 23 wrapped over the spacer. The barrier 23 may comprise asbestos paper or some other suitable material.

The cooling ducts between the barrier 23 and the high voltage section 16 are preferably obtained by the use of a, plurality of single glass rods 24 spaced around the barrier with each single rod 24. disposed directly over each pair of glass rods 18' so as to rest in the pocket formed between the pair of rods 18 in the underlying layer. With this. construction, the single glass rods 24 have less tendency to move or shift. The single rods 24' are. also preferably enclosed by a sleeve 25 of Fiberglas fabric.

The high voltage winding section 16' which may be of any suitable designknown in the; art surrounds the low voltage Winding and completes the winding assembly.

In, actual assembly of. transformer 11 shown in Figs. 1', 2 and 3, the low voltage section 15 may be manufactured as follows;

First the form 21 of, the proper diameter is selected which provides. sufiicient clearance from the core leg 14 to withstand dielectric stresses which might occur, as well as. to. permit the free flow of. cooling, medium over the core. The form 21 may be made of any suitable material having the required thermal and dielectric prop: erties, asbestos paper being quite satisfactory. The form 21 is. placed in a winding lathe and the spacers which comprise the pair of glass rods 18 covered by sleeve of Fiberglas material are disposed. on the. cylindrical surface of the. form 21 and temporarily attached thereto by means of any suitable material such as glass tape. The low voltage coil 17a is then wound directly over the glass spacing sticks 18 thereby providing the passage or duct 19 between the form 21 and the. first. coil 17aof the low voltage winding section. 15. The second coil 17b is wound directly over the first. coil 17.11.. The. next step. is the. provision, of the cooling duct 19 between the low voltage section- 15 andthe high to low barrier 23. This is accomplished by disposing the spacing sticks 18 on the: cylindrical surfaces of the outer coil 17b of the low voltage section 15 and. temporarily taping them in position. The high to low barrier 23. is then wrapped over the spacing sticks 18 providing a cooling duct 19 between the barrier 23 and the coil 17b. The assembly is then removed from the winding lathe and given a varnish treatment, either a silicon or a phenolic varnish, depending on the class of insulation desired. The purpose of the varnish treatment is to impart mechanical strength to the coils. If desired, the low voltage winding may be subjected to a drying out process prior to the varnish process.

The low voltage section 15 is placed on the winding leg 14 and secured in place by suitable means such as ebony asbestos or asbestos millboard blocks 28. The single glass rods 24 each covered by a Fiberglas fabric sleeve 25 are next situated on the outside of the high to low barrier 23 and are held in place temporarily by means of glass tape. The high voltage coils 22 are then inserted over the low voltage section 15 and a snug fit is obtained by means of wedging strips (not shown).

When both sections of the high voltage and low voltage windings are disposed on the legs 14 of the core 11, the top yoke 29 of the transformer 11 is then clamped in place to complete the assembly.

While only one embodiment of the present invention has been illustrated and described, it will be apparent to those skilled in the art that modifications may be made therein without departing from the scope of the invention or from the spirit of the appended claim.

It is claimed and desired to secure by Letters Patent:

A spacing, means for providing cooling ducts between two cylindrical coils of a stationary induction apparatus having an insulating barrier in spaced relationship between said coils comprising: a first plurality of pairs of cylindricalglass rods disposed parallel to the axis of said coils and spaced circumferentially around the surface of said first coil and said barrier, each said pair of rods covered by a separate sleeve of material made substantially from glass fibers; a second plurality of single cylindrical glass rods disposed parallel to the axis of said coils and spaced circumferentiall-y around the surface of said barrier and said second coil with each of said single rods having its axis equidistant from the axes of an adjacent said pair of rods, each said. single rod being covered by a separate sleeve of said material.

References Cited in the file of this. patent.

UNITED STATES PATENTS Winship Apr. 2, 1929 Johnston Ian. 18, 1949 poration, Catalogue No. EL44.-7, 1 94.4, pages 22-23 relied on. (Copy in Div. 69.). 

